What Environmental Conditions Reduce Predation Vulnerability for Juvenile Colorado River Native Fishes?

Abstract

The incompatibility of native Colorado River fishes and nonnative warm-water sport fishes is well documented, with predation by nonnative species causing rapid declines and even extirpation of native species in most locations. In a few rare instances, native fishes can survive and recruit despite the presence of nonnative warm-water predators, indicating that specific environmental conditions may help reduce predation vulnerability. We experimented with turbidity, artificial blue water colorant (artificial turbidity pond treatment), woody debris, rocks, and aquatic vegetation in a laboratory setting to determine whether any of these types of cover could reduce predation vulnerability and confer survival advantages for juvenile Bonytail Gila elegans (mean = 70 mm total length), Roundtail Chub Gila robusta (mean = 35 mm total length), Humpback Chub Gila cypha (mean = 67 mm total length), and Razorback Sucker Xyrauchen texanus (mean = 74 mm total length). We exposed selected species of juvenile native fishes to predation by adult Largemouth Bass Micropterus salmoides, Smallmouth Bass Micropterus dolomieu, Green Sunfish Lepomis cyanellus, Flathead Catfish Pylodictis olivaris, and Black Bullhead Ameiurus melas in overnight trials. Razorback Suckers served as prey in trials conducted with Largemouth Bass and Black Bullhead. Bonytail served as prey in trials conducted with Largemouth Bass and Flathead Catfish. Roundtail Chub served as prey in trials conducted with Smallmouth Bass and Green Sunfish. We matched sizes of predator and prey so that the maximum body depth of the prey never exceeded 40% of the maximum anatomical gape of the predators. Turbidity of 500 nephlometric turbidity units reduced effectiveness of sight-feeding predators such as Largemouth Bass, Smallmouth Bass, and Green Sunfish by up to 50% but also increased predation vulnerability to non–sight-feeding predators (Flathead Catfish and Black Bullhead) by up to 55%. Turbidity was the only treatment that significantly altered predation mortality of native fish. These results may help explain recent patterns of wild juvenile native fish recruitment to adult life stages at the Colorado River inflow in to Lake Mead and at the inflow of the San Juan River into Lake Powell. Both areas possess abundant introduced predatory fishes but are also very turbid.

Use of trophic ecology of omnivorous fish and abiotic factors as supporting tools for assessing environmental impacts in a neotropical river

“…The BRT model exhibited a higher relative contribution to turbidity (58.28%). Turbidity is a factor that contributes to the protection of juveniles; on the contrary, it also serves as a facilitator for predators, allowing them to hide in high turbidity, and facilitating food intake (Ward & Vaage, 2019), as indicated by our results. In addition to its connection with catfish diet (Tesfahun, 2018), turbidity is typically associated with the water's nutrient content (Damar et al, 2020).…”

Can spatial and temporal differences in fish assemblage structure inform conservation of an endangered sucker in a large western reservoir?

“…Within Lake Mead, two species that were present in relatively high abundance at the Colorado River Inflow and Echo Bay could potentially contribute to lower abundance of juvenile Razorback Sucker at those sites. The Yellow Bullhead was the eighth most abundant species at the Colorado River Inflow, and these fish are effective predators in turbid environments (Ward and Vaage 2019). Similarly, Smallmouth Bass was the ninth most abundant species at Echo Bay; only 130 individuals were captured over the entire time series, and 86% of them were captured at this site.…”

Quantifying Consumption of Native Fishes by Nonnative Channel Catfish in a Desert River

“…2011). Sight‐feeding predators have decreased foraging success with increased turbidity, while non‐sight‐feeding benthic predators have increased success with increased turbidity (Ward and Vaage 2019); catfish have optimal feeding in turbid waters due to their specialized taste organs (i.e., barbels; Grover‐Johnson and Farbman 1976; Morais 2017). Alternatively, increased feeding by Channel Catfish under turbid conditions could occur because prey fish are less aware that predators are present (i.e., due to a lack of visual cues; Abrahams and Kattenfeld 1997) or because there is increased mortality of fish prey in highly turbid waters (Wilber and Clarke 2001).…”

“…Water turbidity has differential impacts on foraging success depending on the predator species (De Robertis et al 2003;VanLandeghem et al 2011). Sight-feeding predators have decreased foraging success with increased turbidity, while non-sight-feeding benthic predators have increased success with increased turbidity (Ward and Vaage 2019); catfish have optimal feeding in turbid waters due to their specialized taste organs (i.e., barbels; Grover- Johnson and Farbman 1976;Morais 2017). Alternatively, increased feeding by Channel Catfish under turbid conditions could occur because prey fish are less aware that predators are present (i.e., due to a lack of visual cues; Abrahams and…”